Direct Examination Of Polymer Degradation By Gas Chromatography .2. Development Of Technique For Quantitative Kinetic Studies

The following difficulties may be encountered when direct-pyrolysis gas chromatography is aplied to obtain quantitative kinetic measurements: (a) poor reproducibility of the measurements, arising from the method of mounting the sample, (b) time and temperature errors, arising principally from the pre-effect of the temperature/time profile of the filament, and (c) dependence of the observed degradation rate on sample thickness, even for samples in the microgramme range. The first two problems have been surmounted by depositing the sample within a limited region of a ribbon filament, and supplying an initial current boost to bring the filament to the desired degradation temperature within one second. If in addition the degradation is effected in the carrier-gas stream of a capillary column GLC apparatus incorporating a detector sensitive to better than 10 −10 g, the pyrolysis may be studied under conditions where the rate becomes independent of sample thickness, i.e. 5 × 10 −8 g samples, 200 Å thick. The requirements of the technique and the choice of operating conditions are described. The principal advantages of the method are that only submicro samples are required, and that quantitative kinetic measurements over a wide temperature range may be performed rapidly.